add waypoint payload parser

app/src/main/java/com/geeksville/mesh/DataPacket.kt

@@ -55,6 +55,12 @@ data class DataPacket(
         else
             null
 
+    val waypoint: MeshProtos.Waypoint?
+        get() = if (dataType == Portnums.PortNum.WAYPOINT_APP_VALUE)
+            MeshProtos.Waypoint.parseFrom(bytes)
+        else
+            null
+
     // Autogenerated comparision, because we have a byte array
 
     constructor(parcel: Parcel) : this(